KANSAS CITY, Mo. — When Colby Rasmus left St. Louis, it was with a boot in the backside after having gotten on the wrong side of Tony La Russa. He preferred to ask his father for help with his swing rather than the team’s hitting coach, Mark McGwire.

Rasmus was traded from St. Louis to Toronto, and when he left after three and a half years as a free agent, it was with little affection. The country boy who grew up in rural Georgia found it as hard to feel at home north of the border as it was to find a place to park his pickup trucks.

When Rasmus signed a one-year, $8 million contract with the Houston Astros last winter, it may not have been a long-term commitment, but he had found a place where he could let his shoulder-length hair down.

“I’d say this has been the best place for me,” Rasmus said Tuesday after the Astros worked out in preparation for the deciding game of their American League division series against the Kansas City Royals. “The environment’s been good — a lot of young guys with a lot of life to them, and not a lot of big egos in the room. I just like to play baseball. I don’t like having too many people put their pressure down on me. I just like to play. That’s helped me.”

Rasmus, 29, once one of the most promising prospects in baseball, is playing like it in the playoffs.

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Rasmus after hitting a solo home run against the Royals in the seventh inning of Game 4.CreditBob Levey/Getty Images

He got the Astros headed in the right direction by clubbing a solo home run off the Yankees’ Masahiro Tanaka in their 3-0 wild-card win at Yankee Stadium last Tuesday, and he has continued to be a menace against the Royals. Rasmus is batting .500 with four home runs, six runs batted in, four runs and six walks (two intentional) in five playoff games.

“I love the calmness that’s around Colby right now,” Astros Manager A. J. Hinch said. “He knows exactly what he wants, exactly when he wants it and, if he gets it — we call him Skinny Pop for a reason. He’s got a ton of power.”

That Rasmus ended up with the Astros was no accident.

Astros General Manager Jeffrey Luhnow, the Cardinals’ former scouting director, made Rasmus his first pick, 28th over all, in his first draft, in 2005.

“I always figured if you put Colby in the right environment, with the right manager and the right teammates, that he would flourish,” Luhnow said. “He’s a colorful character, from the South, who dresses a unique way. I think Colby wants to feel able to express himself and be accepted for who he is.”

Rasmus speaks in a syrupy slow drawl and is more selective with his words than he is at the plate. His hairstyles have carried a broader range, beginning with his first star turn, as a bleach-blond pitcher who helped Phenix City, Ala., to the championship game of the 1999 Little League World Series. He arrived in St. Louis 10 years later with a buzz cut. He experimented briefly with cornrows in Toronto. Now he wears his brown curly hair down to his shoulders.

He is most expressive with his wardrobe, which when he left the clubhouse after Monday’s crushing Game 4 loss included a black circular-brimmed hat, like one worn by the musician Stevie Ray Vaughan. When he wears a long-sleeve shirt, it is invariably buttoned all the way to the neck. Barely a day goes by in the off-season when Ramus, an avid hunter and fisherman, is not dressed in camouflage.

“Whatever I see that I like, I wear,” Rasmus said after removing white-framed sunglasses that he wore during the workout. “I’ve always kind of been that way. As people, we should be able to have our own tics and rhythms. If you want to wear that funky-looking hat, then you wear that funky-looking hat. I guess you could say I’m somewhat of a free spirit. I am who I am.”

Clubhouses can be a difficult place to maintain that distinctiveness, especially the one that Rasmus walked into in 2009 as a ballyhooed 22-year-old rookie on a team chock-full of veterans, who, like La Russa, had strong ideas about how the game should be played.

Rasmus, who now is married and has two young daughters, shared an apartment across the street from Busch Stadium with another free-spirited player, Brendan Ryan. The refrigerator was stocked with boxes of Uncrustables, the packaged crustless sandwiches, and sport drinks. The freezer was full of ice cream bars. The rest of the place was a mess.

“He’s a different guy, and I loved that about him,” said Ryan, who was traded to Seattle after the 2010 season. “I don’t think he’s a guy that’s trying to fit in anywhere, but I think things got tougher and tougher in St. Louis, and he felt isolated. I hope the world is starting to see this guy blossom.”

Those experiences explain why Rasmus, though he is one of the more experienced Astros, is careful in doling out advice, be it on intricacies of the game or how the team should carry itself after Monday’s crushing loss, in which the Astros blew a four-run lead.

“People try to get you to do what they want you to do instead of what you feel is good for you to do,” Rasmus said. “That’s the nature of the beast. For us as baseball players, it’s up to us to decipher what goes into our minds.”

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Rasmus, 29, signed a one-year contract with the Astros last winter.CreditThomas Shea/USA Today Sports, via Reuters

Rasmus was the oldest of four boys, including Cory, 27, a pitcher in the Los Angeles Angels system. The boys grew up in a singlewide trailer outside Columbus, Ga., in the southwest part of the state. About all they wanted to do was play baseball, and their father, Tony, coached them through Little League and in high school, where in 2005 they won the state championship and were declared by Baseball America as the top high school team in the country.

It was about as far from a major league clubhouse as it was from Manhattan.

“I was a rough kid, beating up my brothers and fighting all the time,” Rasmus said. “I grew up in a sheltered home. My dad ruled with an iron fist. We didn’t really live to where other people were able to put their influence on us. It was my dad’s way, and that’s how we lived. So to come into an environment like this where people are jealous and telling you what to do all the time, it was a shock. I didn’t know how to handle it.”

Luhnow watched Rasmus play in high school, then spent more time getting to know him when Rasmus went to work out in Memphis. It was an odd pairing — the country boy and the cosmopolitan Luhnow, who grew up in Mexico City, graduated from the Wharton Business School and was hired by the Cardinals with little background in baseball.

“Colby was sort of the face of the new methods the Cardinals were using, so he and I became linked whether we liked it or not,” said Luhnow, whose analytics-driven approach has helped turn the Astros around. “When you’re a scouting director and you make your very first pick in the first round, there’s a lot of pressure to have that player make it to the big leagues and not just make it but have an impact. So I definitely felt it.”

Knowing Rasmus and knowing why he left St. Louis and was eager to leave Toronto, Luhnow thought he would fit in. Rasmus also listened to offers from others, including Baltimore. He will be a free agent again after this season, and Luhnow acknowledges that Rasmus may be playing himself into a contract above what the Astros would be willing to pay. Asked if he felt that same connection to Luhnow, Rasmus shrugged.

“I don’t get that sentimental,” he said. “The best way I could explain it is I wanted to come in this year and play hard for him.”

A version of this article appears in print on , on Page B14 of the New York edition with the headline: A Free Spirit Discovers His Place, and a Postseason Stroke, With the Astros. Order Reprints | Today’s Paper | Subscribe